Apparatuses disclosed in, for example, Patent Document 1 are known as the superheated steam generator arranged as described above. FIGS. 1a to 1c show, as an example of the apparatuses, a structure of a superheated steam generator main body 10 having a plurality pipe members disposed in parallel with each other, the hollow portions of the pipe members being used as steam passages, and the pipe members themselves being used as heating elements, wherein FIG. 1(a) is a left side elevational view, FIG. 1(b) is a front elevational view from which insulators are removed, and FIG. 1(c) is a front elevational view in longitudinal cross-section of the pipe members 13 acting as heating elements and corrugated sheets 15 acting as interference members.
The superheated steam generator main body 10 (refer to FIGS. 11(a) and 11(b)) is composed of an introduction section 11 to which saturated steam is supplied, a heating section 12 for heating the saturated steam and converting it into superheated steam, and a discharge section 16 for discharging the superheated steam. The introduction section 11 and the discharge section 16 are composed of a funnel- or bugle-shaped cylindrical body to change the diameter of a steam passage. The heating section 12 includes the plurality of pipe members 13 disposed in parallel with each other and an induction coil 17 comprehensively wound around a group of the pipe members 13 through a not shown insulators. The pipe members 13 are composed of a conductive material that is induction-heated by electrifying the induction coil 17 with high frequency, and the one ends of the pipe members 13 communicate with and connect to the introduction section 11, the other ends thereof communicate with and connect to the discharge section 16, and the hollow portions 14 act as stream passages. Note that, in the superheated steam generator main body 10, the pipe members located in the outer peripheral region of the pipe group are composed of non-magnetic stainless steel and those located in the inner deep region thereof are composed of ferromagnetic carbon steel, thereby the induction heating action is executed uniformly by the induction coil 17.
The corrugated sheets 15 are disposed in the hollow portions 14 of the pipe members 13 (refer to FIG. 11(c)) as interference members (turbulence generation means) for disturbing the flow in the stream passages. The corrugated sheets 15 are repeatedly bent over almost the entire length of the pipe members 13 at the same pitch and at the same angle.
The induction coil 17 (refer to FIG. 11(b)) is also wound over almost the entire length of the heating section 12 at the same pitch. Note that there is also an apparatus in which a moisture steam generation function and a moisture steam superheat function are accommodated in a series of zone (for example, refer to Patent Document 2). In the above apparatus, however, although the winding density of the induction coil is increased in an aquiferous zone to which evaporation latent heat must be supplied, the induction coil is wound at the same pitch in a space zone in which moisture steam passing therethrough is further heated and made to superheated steam.
The superheated steam generator main body 10 is used as a superheated steam source for processing, for example, waste oil, waste plastic, kitchen refuse, food, equipment, and the like for the drying, reduction in volume, cocking, sterilization, and the like of them, thereby superheated steam is used in an increasing volume. In many case, the superheated steam generator main body 10 has a temperature control circuit affixed thereto to supply superheated steam of a temperature suitable for an object of use. A temperature control is executed by a feedback control by a PID operation (proportional/integral/differential) which can be used easily when there is only one object to be controlled, and the induction coil 17 is subjected to such a power control that a temperature of the to be controlled object is detected and the detected temperature is set to a target temperature. The temperature to be controlled is ordinarily a discharged steam temperature or a temperature of a processing section disposed behind the discharge section.
FIGS. 12(a) to 12(c) show an example when a discharged steam temperature is feedback-controlled, wherein FIG. 12(a) is an overall block diagram including a temperature control circuit and other associating apparatuses, FIG. 12(b) is a block diagram of the temperature control circuit, and FIG. 12(c) is a time chart of a temperature change after heating starts.
The superheated steam generator main body 10 (refer to FIG. 12(a)) has a heating element thermometer 21, a discharged steam thermometer 22, and a temperature control circuit 23 affixed thereto. The heating element thermometer 21 is composed of, for example, a thermocouple, is attached to the pipe member 13 acting as the heating element at the position approximately the center of the axial direction of the pipe member 13 with respect to both the outside surfaces thereof. The thermometer 22 detects the temperature of the heating element and sends the detected temperature Ta to the temperature control circuit 23. The discharged steam thermometer 22 is also composed of, for example, a thermocouple and attached to the discharge section 16 or to a superheated steam supply pipe and the like just downstream of the discharge section 16. The thermometer 22 detects the temperature of the superheated steam discharged from the superheated steam generator main body 10 and sends the detected temperature Tb to the temperature control circuit 23.
The temperature control circuit 23 (refer to FIG. 12(b)) is simply embodied using a temperature regulator (for example, a commercially available electronic temperature regulator) in which an alarm issue comparison operation circuit (CMP.) and a follow-up control PID operation circuit (PID) are assembled in one package. The temperature regulator includes each two sets of manual reference temperature setting means and external signal input means and is arranged such that one set value and one external signal are input to the comparison operation circuit, and the other set value and the other external signal are input to the PID operation circuit. The PID constants of the PID operation circuit, that is, a coefficient of proportion, a coefficient of an integration term, and a coefficient of a differential term can be also set manually or automatically (automatic tuning).
The temperature control circuit 23 employing the above arrangement is arranged such that a heating element upper limit temperature Sa is set to the comparison operation circuit (set value), a detected temperature Ta of the heating element thermometer 21 is input to the comparison operation circuit as an external signal, and when the detected temperature Ta exceeds the heating element upper limit temperature Sa, the comparison operation circuit issues an alarm signal Aa. Further, the temperature control circuit 23 is arranged such that a discharged steam target temperature Gb is set to the PID operation circuit, a detected temperature Tb of the discharged steam thermometer 22 is input to the PID operation circuit as an external signal, and a power command Ia is output from the comparison operation circuit so that a high frequency power supply 24 outputs a coil current Ib for causing the detected temperature Tb to approach the discharged steam target temperature Gb.
The power command Ia and the alarm signal Aa are sent from the temperature control circuit 23 to the high frequency power supply 24 which outputs the coil current Ib according to the power command Ia to the induction coil 17 of the heating section 12 of the superheated steam generator main body 10 as well as forcibly stops the output of the coil current Ib when the alarm signal Aa becomes significant.
In addition to the above-arrangement (refer to FIG. 12(a)), a saturated steam generator 25 is disposed upstream of the superheated steam generator main body 10 to supply saturated steam, and a superheated steam processing apparatus (superheated steam applicator) 26 is disposed downstream of the superheated steam generator main body 10 to execute processing using superheated steam.
When the superheated steam generator main body 10 arranged as described above is operated, first, the heating element upper limit temperature Sa, the discharged steam target temperature Gb and the PID constants are set to the temperature control circuit 23. The heating element upper limit temperature Sa is determined by materials and the like of the pipe members 13, and, when general-purpose austenitic stainless steel and carbon steel are used, it is set to, for example, about 600° C. to 650° C. The discharged steam target temperature Gb is determined by the specification required by the superheated steam processing apparatus 26 and set to, for example, about 200° C. to 500° C. within the range lower than the heating element upper limit temperature Sa according to a purpose of use and a state of use. Although the PID constants are fundamentally determined by the operation characteristics of the superheated steam generator main body 10 and the high frequency power supply 24, they are also adjusted in a site because they are affected by an amount of steam supplied from the saturated steam generator 25 and a temperature of steam discharged to the superheated steam processing apparatus 26.
When the superheated steam generator main body 10 and the like are operated, saturated steam is supplied from the saturated steam generator 25 to the superheated steam generator main body 10 and made to superheated steam by being heated by the superheated steam generator main body 10, and the superheated steam is supplied from the superheated steam generator main body 10 to the superheated steam processing apparatus 26, and desired processing is executed by the superheated steam processing apparatus 26 using the superheated steam.
At the time (refer to FIG. 12(c)), when the PID constants are appropriately set and the amount of steam is within an appropriate range, an appropriate electrification command Ia is output from the temperature control circuit 23 to the high frequency power supply 24. In response to the command, an appropriate coil current Ib is flown from the high frequency power supply 24 to the induction coil 17 of the superheated steam generator main body 10. Accordingly, the detected temperature Tb of the discharged steam thermometer 22 becomes equal to the discharged steam target temperature Gb, and the detected temperature Ta of the heating element thermometer 21 remains less than the heating element upper limit temperature Sa as long as the discharged steam target temperature Gb is not set constrainedly (refer to a solid line graph of FIG. 12(c))
FIGS. 13(a) to 13(c) show an example when a discharged steam temperature is feedback-controlled, wherein FIG. 13(a) is an overall block diagram including the temperature control circuit and other associating apparatuses, FIG. 13(b) is a block diagram of the temperature control circuit, and FIG. 13(c) is a time chart of a temperature change after heating starts.
These figures are different from the figures described above (FIGS. 12(a) to 12(c)) in that a processing section thermometer 27 is provided in placed of the discharged steam thermometer 22 and the temperature control circuit 23 is replaced with a temperature control circuit 28 in correspondence to that a to-be-controlled object is changed from a discharged steam temperature to a processing section temperature.
Although the processing section thermometer 27 is also composed of, for example, a thermocouple, it is affixed to the superheated steam processing apparatus 26 (refer to FIG. 13(a)), detects, for example, a steam temperature in a processing chamber or a wall temperature of the processing chamber that is a substitute of the steam temperature and sends the detected temperature Tc to the temperature control circuit 28.
Although the temperature control circuit 28 (refer to FIG. 13(b)) is also embodied by the same temperature regulator as the temperature control circuit 23 and an alarm issue comparison operation circuit (CMP.) is used likewise, a follow-up control PID operation circuit is used differently. More specifically, as to the comparison operation circuit, the heating element upper limit temperature Sa is set to the circuit likewise and the detected temperature Ta is set thereto as an external signal likewise, and when the detected temperature Ta exceeds the heating element upper limit temperature Sa, an alarm signal Aa is issued. As to the PID operation circuit, however, a processing section target temperature Gc is set to the circuit, the detected temperature Tc of the processing section thermometer 27 is set thereto as an external signal, and a power command Ia is output from the PID operation circuit so that the high frequency power supply 24 outputs a coil current Ib for setting the detected temperature Tc as the processing section target temperature Gc. The command and the like Ia, Aa are sent to the high frequency power supply 24 likewise the above example (refer to FIG. 13(a)).
Also in this case, when the superheated steam generator main body 10 and the like are operated, saturated steam is supplied from the superheated steam generator 25, superheated steam is supplied from the superheated steam generator main body 10, and processing is executed by the superheated steam processing apparatus 26 using the superheated steam. At the time (refer to FIG. 13(c)), when the PID constants of the temperature control circuit 28 is appropriately set and an amount of steam is within an appropriate range, an appropriate electrification command Ia is output from the temperature control circuit 28 to the high frequency power supply 24. Accordingly, an appropriate coil current Ib is flown from the high frequency power supply 24 to the induction coil 17 of the superheated steam generator main body 10, the detected temperature Tb of the processing section thermometer 27 is set to the processing section target temperature Gc, and the detected temperature Ta of the heating element thermometer 21 remains less than the heating element upper limit temperature Sa (refer to a solid line graph of FIG. 13(c)).
[Patent Document 1] Japanese Patent Application Laid-Open Publication No. 2002-270351 (page 1, FIG. 3)
[Patent Document 2] Japanese Patent Application Laid-Open Publication No. 2003-297537 (page 1)